ETA 2681 caliber: dimensions and drop-in group

Used in: the slightly larger small ladies automatic, a size up from the 2671.

A compact automatic with date at 19.40 mm x 4.80 mm, a size larger than the 2671. The two share a family but not a diameter, so a 2671 case will not take a 2681 without a case change.

Drop-in group: 8 3/4 ligne small automatic (19.40 mm x 4.80 mm). Matching diameter and height is necessary but not sufficient. A donor is only a true drop-in when the dial-foot positions, hand-hole sizes, stem length and calendar layout also match. Two movements can share a case and still need a new dial, re-broached hands or a cut-to-length stem.